Method of treating ores



Jan. 13,1942. R. B. LADoo E-rAl. 2,269,912

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Patented Jan. 13;, 1942 METHOD F TREATING ORES i RaymondB. Ladoo, Newton, ,Mass., and William G. Hubler, Duparquet, Quebec, Canada Application January 4, v19.29, serial No. 249,330

(ci. ssa- 94) 2 Claims.

This invention relates to a method of treating ores, and more particularly has reference to a method of preparing an ore where it is desired that the nal product be free from iron-bearing impurities or where it is desired that the product be relatively closely sized. It nds especial application in the preparation of nepheline syenite for industrial purposes, although it Awill be readily appreciated that it is capable of use in the treatment of other ores.

One of the prime purposes in the preparation of certain ores, such as for instance nepheline syenite, is the elimination, or at any rate reduction in amount, of iron-bearing impurities in the final product. The major portion of such impurities occur naturally in the original or crude ore, but heretofore there have been appreciable amounts of iron incorporated in the ore during the process of treatment. The prior processes and apparatus for the preparation of nepheline syenite have not been successful in extracting the maximum amount of the original iron-bearing impurities from the ore, and in most instances there have been added to the ore certain iron particles which are supplied, by attrition, from f the equipment in which the ore'is treated.

Likewise, considerable diiculty has Aheretofore been experienced in crushing ore to a certain desired size without at the same time producing an excessive amount of fines.

One of the objects of this invention is to provide a process and apparatus for the reduction of an ore to a desired size. Another object of our invention is to reduce an ore to a desired size while maintaining the production of nes at a minimum.

Still another object of our invention is to provide a process and apparatus for reducing an ore to a predetermined size, and at the same time inhibiting the introduction of impurities, particularly iron-bearing impurities, to the ore.

To accomplish the above, and other important' objects as will appear more fully hereinafter, our invention in general embraces the reduction of ore to the desired particle sizes in such a way that there is no over-size and a minimum of undersize of nes. Also comprehended in the preferred form of the invention is the securing of the desired particle-size by means which inhibit the introduction of impurities to the ore. More specically, the ore fed to the grinding mill, or mills, is first properly sized and then choke-fed to the mill, the ore preferably being kept out of contact with iron in the nal stage of reduction. Inthe preferred form of my invention the ore screenings from a jaw crusher are choke-fed into a roll mill, the rolls of which are so spaced that there is a low ratio of reduction between the spacing of the rolls of the mill and the spacing of the jaws of the crusher; and further reduction is secured by choke-feeding the material from the roll mill to a pebble mill lined with a nonferrous material and provided with pebbles of material similar to the ore being treated, the rate of passage of the material, in combination with the type of grinding media and' the chokefeeding, being such as to maintain the production of iines ata minimum. All of the foregoing may or may not be preparatory to a treatment for the removal of impurities.

In the accompanying sheet of drawings we have illustrated one specific embodiment of our invention, but it is to be distinctly understood that the precise -ilow sheet and pebble mill may be departed from in certain respects without exceeding the inventive concept as dened in the appended claims.

In the drawing:

Figurev 1 is a flow sheet which illustrates the preferred form, and one alternative form, of our invention.

Figure 2 is a diagrammatic showing of a type of pebble mill which is well adapted for use in our process.

Referring particularly to Figure 1, it will be observed that the crude ore, which may be nepheline'syenite for purposes of illustration, is fed to a jaw crusher I where the ore is crushed to a maximum size of one-half or three-eighths of an inch. Of course, equipment other than a. jaw crusher may be employed to reduce the crude ore to the desired size, but in practice we have found a jaw crusher preferable.

The product of the jaw crusher I is then screened as at 2, the screening device preferably being of an eight-mesh size. The over-size from the screen passes to a bin 3, and the undersize to a bin 4.

The bin 3 is of a size suitable to hold a suicient quantity of crushed ore to permit chokefeeding in the next succeeding step. When a suicient amount of ore has initially accumulated in bin 3 for this purpose', it is then chokefed into a roll lmill 5. In this mill the rolls are spaced approximately one-quarter inch apart. With the jaw crusher I crushing to one-half or three-eighths inch, and the rolls of mill 5 being spaced one-quarter inch, it will be observed that a low ratio of reduction is provided. It will of course be appreciated that a vlow ratio of reduction may be obtained even when the rolls are spaced closer together, provided the jaw crusher product is 4proportionately reduced, whether by closer spacing of the jaws or by the use of a scalping screen, etc.

The roll mill 5 is in closed circuit with the eight-mesh screen 2, and that portion of the roll mill product in excess of eight-mesh is returned to the bin 3. In view of the fact that the space between the rolls is so much greater than the screen openings, there is a large percentage of screen over-size reject to be returned to the rolls, and consequently a heavy circulating load through the roll mill 5. i

The foregoing operation results in the reduction of the ore to a minus eight-mesh size, and

at the same time the formation of nes is helcl at a minimum and the addition of iron impurities is inhibited.

As indicated in Figure 1, the ,under-size from screen 2 is passed to bin t, which feeds the ore to a twenty-mesh screen 6. The plus twentymesh material from screen 6 is'choke-fed to pebble mill l. This pebble mill departs from the conventional type in certain respects, and in Figure 2 there is diagrammatically shown a mill that is particularly well adapted for use in our process. The mill 'l is for the purpose of reducing the size of the plus twenty-mesh material, but at the same time is designed to avoid, or minimize, the production of nnes and the incorporation of ferrous impurities into the ore being treated.

Referring more particularly to Figure 2, the mill may be formed with a casing il of conventional construction, and provided with a feed trunnion il and a discharge trunnion It) of such a size as to permit of a heavy and rapid circulating load. A grating Il is .located in the mill adjacent the discharge trunnion in order to retain the pebbles in the mill but permit the discharge of the ground ore.

The casing li is lined with a non-ferrous material l2, suchas silex, and the grinding media are non-ferrous pebbles I 3. These pebbles are preferably pieces of the ore that is being treated, and initially may be from 4 to 6 inches in size. Of course, as these pebbles are broken down during the course of operation, they may be replenished.

The pebble mill 'i is in closed circuit with the twenty-mesh screen 6, and such portions of the pebble mill product as is in excess of twentymesh is returned to the mill. The operation of the mill is controlled to secure a rapid passage of material through the mill (in order to secure a maximum of twenty-mesh and a minimum of fine dust) which, in conjunction with the screen 6, results in a heavy circulating load.

It will therefore be seen that the pebble mill 1 eects a reduction in size of the ore fed to it, and at the same time inhibits the formation of nes and the addition of impurities to the ore.

The under-size from screen 6 passes to a fiftymesh screen lli where the material is sized to minus fifty-mesh and plus fifty-mesh. The respective screenings are passed through magnetic separators l5 and i6 where the iron particles and other magnetic impurities in the ore are removed, the concentrates being sent to storage bins l1 and t8, respectively.

One alternative to the foregoing process may he made by omitting the screen fand roll mill li,

and passing the product from the jaw crusher directly to bin 4 as indicated by dotted line I9. In this case 1t may be necessary to decrease the spacing of the jaw crusher l so that the crusher will produce, for instance, a one-quarter inch product, although the necessity for such a modification of the crusher will depend upon the condition of the particular ore being treated.

It will be observed from the foregoing that we have devised a process for the treatment of ores that is of particular application where there is sought a final product free from iron-bearing impurities, and especially where such product is obtained by magnetically separating the impurities from the ore. It is Well known that the presence of nes impedes the operation of magnetic separators (and for other reasons, nes may be undesirable), and our process produces ore particles of the size best suited for magnetic separation and with a minimum of fines. Fur thermore, the process is carried out, and partic ularly the grinding stage, in such a way that little, if any, iron is introduced to the ore during the course of treatment.

It will of course be appreciated that the word iines is a relative term, and in the process described above the final product sought is one of 20 to 100 mesh. By iinesf we have in mind particles of a size less than mesh, but it is obvious from the foregoing that the exact size for any particular operation may be controlled as desired.

While we have described one specific process, and referred to a preferred type of pebble mill, it is to be understood that we are to be limited only by the scope of the appended claims. It is also to be understood that, while we have referred specifically to the application of our invention to nepheiine syenite, it may be used for any ore presenting similar problems.

We claim:

1. The process of treating syenites containing iron bearing impurities, which comprises reducing the syenite ore with a Crusher, removing the smaller particles of the resulting material with a screen, choke feeding the larger particles between rolls until they will pass through said screen, removing the larger particles of the screen under-size with another screen and feeding these larger particles through a pebble mill having syenite ore as a grinding medium and a non-ferrous lining until they will pass through the second screen, and magnetically separating the iron bearing impurities from said ore.

2. The process of treating syenites containing iron bearing impurities, which comprises reducing the syenite ore with a crusher, separating the resulting product with an eight mesh screen, choke feeding the plus eight mesh screenings into a roll mill until it will pass through the eight mesh screen, separating the minus eight mesh screenings produced by the jaw crusher and the roll mill by means -of a twenty mesh screen, feeding the plus twenty mesh screenings through a pebble mill until they will pass through the screen, separating the minus twenty mesh screenings by means of a fifty mesh screen, and separately treating the products of the lastmentioned screen in magnetic separators to remove the iron bearing impurities from said ore while in such granular condition.

RAYMOND B. LADOO. WILLIAM G. HUBLER 

